A common drill bit used in the exploration and recovery of oil, water and the like to bore through earth formations is the rotary drill bit. In use, the rotary drill bit is secured to the lower end of a string of drill pipe which rotates and urges the drill bit against the underlying earth formation. The drill bit includes a drill bit body and a number of conical rock bit cutters rotatably supported by bearings at the lower pin end of the bit body.
As the drill bit is rotated, the bit cutters bore into the underlying earth formation. Extending radially from each bit cutter are a number of teeth, each having a tip made of diamond or metal that is harder than the underlying earth formation. The bit cutters essentially rolls across the underlying earth formation as the bit rotates, causing the teeth extending from the cutter to create a bore hole by impacting and pulverizing the formation. At the same time, drilling mud is pumped through the drill string and bit body, around the bit cutters, to cool the cutters, lubricate exterior surfaces of the bit and sweep fragments of the pulverized formation from the cutters back to the surface through the space surrounding the drill string and drill bit.
The bearings supporting the rock bit cutter are protected by bearing seals from the highly abrasive mixture of drilling mud and cuttings, which would otherwise quickly destroy the bearings. Typically, bearing seals comprise an O-ring or a bellville spring covered with an elastomeric material. The seal is positioned about the bearing and compressed between the bearing surfaces of the pin end of the bit body and the bearing surfaces of the bit cutter to form a barrier against intrusion of drilling mud and cuttings.
In an effort to extend the service life of such bearing seals in the past, both the bit body and the bit cutter have been manufactured from high quality metals, such as forgings and rolled bar stock. This has allowed the bearing surfaces of the bit body and the bit cutter between which the bearing seal is compressed to be machined to a smooth finish. As the bit cutter rotates during drilling, the bearing seal can slide across the bearing surfaces of the pin end of the bit body and the bit cutter without significant frictional wear.
Unfortunately, use of forgings and rolled bar stock to manufacture the bit cutter is relatively costly. For example, each bit cutter must be machined entirely from a forging or rolled bar stock. The teeth of each cutter are then formed individually. Such machining procedures alone are costly. In addition, the initial cost of forgings and rolled bar stock is relatively great.
The present invention overcomes the foregoing disadvantages by providing a bearing seal that can be used with bit cutters, and other components, manufactured by casting, a relatively quick and inexpensive procedure. Use of cutters manufactured by casting has not been practical due to voids routinely formed during manufacture. As a result of such voids, a smooth surface for engaging the bearing seal cannot be machined on the bearing surfaces. Instead, the voids cause pits to form along the machined surface. Frictional wear of the bearing seal by the pitted surface of the cutter, such as scuffing and abrasion, reduces service life of the seal beyond acceptable limits.
The present invention includes a bearing seal for use with bit cutters, or other rotary components, manufactured by casting. In a rotary drill bit, for example, the seal assembly includes a resilient seal element placed about the bearing surfaces and compressed between the bit cutter and the pin end of the body. The seal element is secured for rotation with the bit cutter to avoid frictional wear which would otherwise be caused by the pitted surface of the bit cutter. The seal element is secured to the cutter in a number of ways, including by use of an annular groove into which the seal element is assembled and/or a suitable adhesive. If the seal element includes an elastomeric surface which abuts the bit cutter, the element may be secured to the cutter frictionally by engagement of the elastomeric surface with the pitted surface of the bit cutter. If desired, the surface of the bit cutter contacting the seal element is roughened to further secure the seal element for rotation with the bit cutter.
In another aspect of the invention, means are provided for reducing wear of the seal element by the bearing surface of the bit body. If desired, the seal element is provided with a metallic finish which engages the bit body. In this instance, the body may also be provided with a replaceable metallic inlay in contact with the abutting metallic surface of the seal element. In the alternative, the bit body is provided with a non-metallic, low-friction inlay which contacts the seal element to minimize frictional wear.